This invention relates to couplings for flexible hose and more particularly to the type of coupling which is permanently attached to the hose, as by crimping.
Couplings for use with reinforced hose in conducting refrigerant fluid in automotive air conditioning systems are required to be compatible with specific materials forming the inner liner of the hose, provided primarily to control the effusion of refrigerant materials into the atmosphere. Nylon liners are one such device used in these air conditioner hoses.
An inner liner of nylon, while providing many attributes in compatibility and control of the refrigerant is especially difficult to grip and seal in a coupling. This is due to the fact that while nylon is somewhat elastic it has a high percentage of delayed recovery at low strain values. That is, the material takes a set in its formed state and tends not to return to its previous condition. This heat set characteristic of nylon acts to contravene the gripping and sealing forces imposed on the material in a crimped coupling resulting in unpredictable cold flow effects. These effects are accentuated in the automotive environment where wide temperature swings, high vibration and pullout forces are encountered.
One prior art solution is described in U.S. Pat. No. 2,453,997 where a massive rubber plug is employed to achieve a seal between the inner liner of refrigerant hose and the shank of a crimped coupling. In this arrangement it is specified that the maximum pressure exerted by the crimped sleeve should be applied over the seal and that preferably the seal is extruded axially into areas between the shank and inner liner. The lining of this hose is a compound of polyvinyl alcohol and due to the relatively uncontrolled deformation of the seal, does not provide a satisfactory coupling for automotive applications.
Another example of prior art coupling for air conditioner applications is described in U.S. Pat. No. 4,198,079 wherein the problem of the junction between the nylon inner liner of a hose and the nipple of a coupling is addressed. This coupling, however, is reusable, employing a nut with a special thread and does not have a separate seal element between the nipple and liner.